Field
The present invention relates to a radiofrequency power amplifier used in a communication appliance of a microwave band or a milliwave band, for example, from several megahertz to several hundred gigahertz for mobile communication, satellite communication, etc.
Background
In conventional power amplifiers, a harmonic circuit which reflects a harmonic of an optimum phase for a transistor is used to improve the power-added efficiency (PAE) of the transistor (see, for example, JP 2012-205246 A, JP 2009-159591 A and JP 2001-53510 A). In the harmonic circuit, there is a need to set an impedance for a short for an even harmonic, such as the second harmonic in the case of class-F operation, and to set an impedance for a short for an odd harmonic such as the third or higher harmonic in the case of inverse class-F operation (see, for example, Akira Inoue and four others, “Analysis of Class-F and Inverse Class-F Amplifiers”, Shingaku Giho, The Institute of Electronics, Information and Communication Engineers (General Incorporated Association), TECHNICAL REPORT OF IEICE ED 2003-214, ED2000-231, p. 29-35). As the harmonic circuit, a capacitor, wire, or open stub is connected to an input or output terminal of the transistor.
In the conventional power amplifiers, a harmonic circuit is provided outside a transistor and, therefore, wires, wiring elements or the like exist between the transistor and the harmonic circuit. A parasitic inductance and a parasitic resistance are caused thereby and it is difficult to set an impedance for a desired harmonic.